Background. The search for cognitive predictors of success in language learning is associated both with basic cognitive characteristics (processing speed and spatial working memory) and with general characteristics (intelligence). However, the ratio between cognitive functioning and success in language learning can change during the period of school education and depends on the socioeconomic level of the society and the effectiveness of the national educational system. Objective. To analyze the cognitive predictors of Russian language learning samples of Russian-speaking 11th graders from Russia, Kyrgyzstan, and Moldova, three countries with a similar organization of the educational system, but differing in the functional effectiveness of that educational system and in their socioeconomic levels. Design. The sample comprised 545 Russian-speaking 11th graders (average age = 17.42 + 0.59; 36.1% male) studying Russian throughout their public-school education in Russia, Kyrgyzstan, and Moldova. The statistical methods of one-way analysis of variance, correlation, and multiple regression analysis were used. Results. Among the indicators of cognitive development we analyzed, the functioning of the national educational system is the one most associated with the development of fluid intelligence of 11th graders, which is directly proportional to the quality of education in the country; to a lesser extent, it is associated with the development of working memory. In Kyrgyzstan (average level of socioeconomic development) and Moldovian (low level of socioeconomical development), only fluid intelligence was associated with the score on the state exam on the Russian language. In Russia, which has a very high level of socioeconomic development, spatial working memory becomes important, along with fluid intelligence. Conclusion. Differences in the relationship between cognitive functioning and success in Russian-language learning are associated both with the objectives of the state exam (identification of pupils ready to attend university versus testing of what was learned in school), and, in conditions of low educational effectiveness, with a greater cognitive load during the exam.